It is known to use ultrasound to image a fetus in the womb by transmission and reception of ultrasound waves from a transducer.
Three-dimensional (3D) ultrasound images may be obtained by using software to combine ultrasound data that has been taken at different positions or angles, and to render an image from the combined data using methods such as simple surface shading or direct volume rendering. In four-dimensional (4D) ultrasound imaging systems, a series of three-dimensional images obtained at different times is dynamically rendered to produce a moving 3D image, for example a 3D ultrasound movie.
In recent years, 3D and 4D ultrasound images have been made more realistic through the use of advanced lighting techniques (referred to as global illumination, gradient free lighting, subsurface scattering or photon mapping) that simulate illumination with a more physically accurate model than was previously used.
Although ultrasound images may in principle be rendered using any color, 3D and 4D fetal ultrasound images are usually rendered in a standard color, a sepia or golden-yellow color.
Many parents are having 3D and 4D ultrasound scans in order to bond better with their unborn child, motivated by the realistic appearance of the scans. 3D or 4D ultrasound scans can also be useful for informing parents of the appearance of a fetus that has an abnormality such as a cleft lip or cleft palate. However, the standard color used to render the images is not realistic.